180 Dr. R. Greeff on Autolytus prolifer. 
fission and gemmation, only that in Nats these occur ve 
regularly ae distinctly in the formation of each new indi- 
vidual. 
To return once more to our figured example (PI. VIII. fig. 2), 
it is evident that the offspring is still firmly united to its 
parent, even by the possession of a common intestine, although 
it is already completely filled with mature ova. ‘This observa- 
tion, however (as indeed has already been indicated by Krohn), 
contradicts the assertion of Frey and Leuckart that the new 
individuals produced by gemmation, so long as they remain 
inserted in the common stock, do not attain such a degree of 
development as to render them capable of the production of 
ova. 
Lastly, as regards the third point to be elucidated, namely 
the establishment of Awtolytus prolifer as a species, | must 
admit that I was at first inclined to think that in the animal 
figured in Pl]. VIII. fig. 1 I had a new species before me. This 
was due in part to the insufficiency of the specific description 
of Autolytus prolifer and the want of accurate figures*. On 
further comparison, however, I cannot resolve upon the esta- 
blishment of a new species, but rather believe that my animal 
coincides with Autolytus prolifer. I also think I may say, 
with probability, that Autolytus cornutus of Agassiz is likewise 
identical with A. prolifer; at least, neither from his descrip- 
tion nor from his figures (which certainly are not sufficient for 
specific determination) have I been able to find any essential 
differences between A. cornutus, A. prolifer, and my own 
specimen. What Agassiz says (/.c. p. 391) as to the differ- 
ences in the number and form of the segments and in the 
number of the long simple bristles, between the progeny of 
Autolytus cornutus and prolifer (Sacconerets helgolandica), ap- 
pears to me to be by no means sufficient for establishing wide 8 
distinction between the primary individuals, as, from the above 
statements with regard to number of segments &c., the pro- 
lificate progeny not only may, but frequently even must, ne- 
cessarily, differ from each other in these respects. 
It is otherwise with the male progeny of an Autolytus known 
under the name of Polybostrichus longosetosus, irst., which in 
all probability represents a species distinct from A. prolifer, as 
the accurate investigations of Keferstein established the exist- 
ence of essential differences, in the structure of its head &c., 
from Polybostrichus Miilleri (Sacconereis helgolandica), the 
male progeny of Autolytus prolifer. | 
* Excellent as 0. F. Miiller’s figure of his Nereis prolifer (Zool. Dan. 
fasc. ii. tab. lii. fig. 6) is for that time, it does not suffice for specific 
determination. : 
